The present invention is related to voltage regulation, and more particularly to systems and methods for improving transient response in a voltage regulator.
Many electronic devices such as, for example, hard disk drives, cellular telephones and notebook computers include a number of semiconductor circuits powered by one or more supply voltages. These supply voltages are often generated by voltage regulators that may in some cases be integrated with the particular semiconductor circuits. The voltage regulators may provide a regulated voltage output that is derived from either battery power or some other power supply.
FIG. 1 shows an exemplary voltage regulator 100 with a number of transistors 132, 138, 142, 148, 152, 158, 162, 168, 172, 178, 182, 188, 192, 198 that are powered between voltage potential VDD 104 and VSS 102. In particular, transistor 132 is an NMOS source follower with a capacitor 125 that couples the gate of transistor 132 to VSS 102. Voltage regulator 100 provides a voltage output 120 to a load 130 that is electrically coupled between the source of transistor 132 and VSS 102. In operation, a voltage reference 110 is applied to the gate of transistor 178, and voltage output 120 tracks voltage reference 110. Capacitor 125 operates to oppose any sudden changes in the voltage at the source of transistor 132 (i.e., voltage output 120). Where the value of capacitor 125 is too small, it is possible for voltage output 120 to ring or oscillate upon any sudden change of either voltage reference 110 or load 130. To avoid the possibility of such oscillation, a relatively large value for capacitor 125 is chosen (e.g., at least two times the value of the Cgs of transistor 132) to hold the gate of transistor 132 steady. This large value for capacitor 125 limits the initial voltage disturbance at voltage output 120, however, the return to a baseline output value is relatively slow as it relies on the transconductance of transistors 172, 178. This transconductance is typically small compared to the gm of transistor 132 for low power operation.
FIG. 1b is a graphical representation 101 of voltage regulator 100 in operation. As shown, voltage regulator 100 is capable of tracking relatively quick changes in voltage reference 110 or load 130 as indicated by operational periods 111, 121, 131. However, the recovery period required to return to a baseline output value is relatively slow as indicated by operational periods 113, 123, 133. Such a slow recovery period may limit the overall switching frequency of a circuit regulated by voltage regulator 100. Such a low frequency may be particularly limiting in storage applications.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced systems and methods for improving response time in voltage regulators.